Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, generally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the fuel cell, in order to supply a fuel gas such as a hydrogen-containing gas and an oxygen-containing gas such as the air to the anode and the cathode of the electrolyte electrode assembly, a fuel gas channel and an oxygen-containing gas channel are formed along surfaces of the separator. The fuel cell stack may adopt internal manifold structure where a fuel gas supply unit and an oxygen-containing gas supply unit extend in the stacking direction for distributing the fuel gas and the oxygen-containing gas to each fuel gas channel and each oxygen-containing gas channel.
For example, in a flat plate type solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-172594, unit cells (not shown) and separators 1 are provided alternately, and as shown in FIG. 22, at four corners of the separator 1 gas supply holes 2a, 3a, and gas discharge holes 2b, 3b extend through the separator 1 in the stacking direction, and a plurality of gas flow grooves 4a and ridges 4b in a plurality of rows are arranged alternately along the surface of the separator 1.
The gas flow grooves 4a are connected to the gas supply hole 2a and the gas discharge hole 2b through triangular recesses 5a, 5b. A throttle section 6 and blocks 7 are provided in a gas inlet section of the triangular recess 5a, near the gas supply hole 2a, as means for limiting the flow rate of the gas. The throttle section 6 and the blocks 7 function to increase the pressure loss of the gas flowing from the gas supply hole 2a to the gas inlet section.
Further, at opposite ends of the gas flow grooves 4a, a shallow gas flow inlet 8a and a shallow gas flow outlet 8b are provided, for functioning to increase the pressure loss of the gas flow.
However, in Japanese Laid-Open Patent Publication No. 10-172594, in the middle of producing or using the separator 1, when foreign materials such as dust are clogged in the throttle section 6, it is not possible to supply the reactant gas from the gas supply hole 2a to the gas flow grooves 4a. Therefore, the whole separator 1 needs to be replaced, and the cost required for production and maintenance of the separator 1 is high.
Further, at the time of stacking a plurality of the separators 1 and unit cells alternately into a stack, it is necessary to reliably seal the gas supply holes 2a, 3a and the gas discharge holes 2b, 3b, and it is necessary to apply a relatively large tightening load to the separators 1. When the relatively large tightening load for sealing is applied to each of the unit cells arranged corresponding to the gas flow grooves 4a and the ridges 4b, the unit cells are excessively pressed. Therefore, the unit cells may be damaged undesirably.